Electrical utilities monitor the electrical energy consumption of customers through electricity meters. Modern electricity meters typically include solid state electronics components and associated electronic devices including sensor devices, data processors, microprocessors, memory devices, clocks, and communications devices. These electronic devices are used for various purposes within the electricity meter, including consumption detection, consumption calculation, data storage, and automatic meter reading (AMR) communications.
In association with these electronic devices, electricity meters also include power supplies configured to provide DC operating power. Typically, the power supply within the meter taps into the AC power line signals that are available within the meter, and converts the AC power line signals to one or more DC voltage levels for use by the meter's electronic devices.
Electricity is provided to customers (and hence to electricity meters) in a variety of voltage levels and service configurations. For example, the nominal voltage delivered to a load may vary from 120 Volts RMS to 480 Volts RMS. The electrical service can be single phase or multiphase, and multiphase services can be delta-wired, or wye-wired. Accordingly, meters must often be configured to accommodate the electrical service and voltage level to which they are connected. Ideally, a single meter may be used for all situations, so as to avoid logistical issues and to improve upon economies of scale. For example, it is more cost effective to build and sell identical meters for uses, than to build and sell multiple different versions of meters, each specific to one of the different electrical services.
However, a single universal meter is impractical for multiple reasons. Nevertheless, the same economies of scale can apply to parts and/or circuits within the meters. Thus, although different meter designs may be required for different electrical services, cost savings can be achieved if many of the same parts or circuits can be used in all or many of the designs. One example is the digital processing circuitry. Electricity meters typically include analog sensing devices that generate measurement signals, an A/D converter that converts the measurement signals to digital signals, and digital processing circuitry that performs the metering calculations using the digital signals. Because digital processing circuitry can be programmed to perform different metering calculations, the same digital processing circuitry can be used in meters for multiple different electrical services.
An area in which multiple designs can be necessary is the power supply. Because the meter power supplies obtain input power from AC power line signals, there is a potential that a different power supply can be necessary for each AC line voltage. To reduce the variety of power supply designs required for meters, it is known to use wide range switching power supplies in meters. By wide range, it is meant that the power supply is configured to receive a range of input voltages. In some cases, a single power supply design can be used for all service voltage levels.
U.S. Pat. No. 7,180,282 shows a wide range power supply that purports to accept input voltages in a range from 96 volts RMS to 528 volts RMS. Because it is not practical to use a switching transistor at such a range of voltages, U.S. Pat. No. 7,180,282 teaches a design that essentially stops the switcher from operating anytime the AC sinusoidal waveform is greater than the threshold. Such a design reduces the maximum available power that would otherwise be available. As a consequence, the power supply must be designed as if it were handling significantly higher power than it would otherwise need, negatively impacting cost, complexity, and size.
An alternative design is to employ power factor correction power supply, in a boost-buck configuration, to generate a low value unregulated DC voltage. One or more voltage regulators can then be used to generate regulated DC bias voltages for digital circuits, displays and the like. In this configuration, the front end circuit is a boost PFC converter that generates a high, but relatively constant, output voltage. A buck converter then reduces the voltage to about 12 volts of unregulated DC. This design does not require a large, high voltage transformer. However, it is not practical to operate the boost converter to a constant output voltage over the large range of input voltages in electricity meters, even excluding the very highest voltage levels of 480 volts RMS. For example, a boost converter that converts a 330 volt RMS input to a 500 volt output cannot efficiently convert a 40 volt RMS input to a 500 volt output. Accordingly, some current designs use two configurations of power supplies to cover potential input voltages ranges from 40 volts RMS to 330 volts RMS. Specifically, first design covers a range of input voltages from 40 volts RMS to 140 volts RMS, and the second design covers a range of input voltages from 85 volts RMS to 330 volts RMS. Such an arrangement, however, requires two different designs to be manufactured, stocked and properly installed in the appropriate meters.
There is a need, therefore, for a power supply that can be used over a wider range of input voltages that avoids some of the drawbacks of the prior art wide-range power supplies.